The f_{D_s} Puzzle

Abstract

Recent measurements of the branching fraction for D_s -> l nu disagree with the Standard Model by around 2sigma. In this case the key aspect of the Standard Model is the calculation of the decay constant, f_{D_s}, with lattice QCD. This talk surveys the experimental measurements, and explains how the lattice QCD calculations are done. Should the discrepancy strengthen again (it was earlier 3.8sigma), it would be a signal of new physics. Models that could explain such an effect are also discussed.

Comments: 7 pp.; 1 fig.; prepared for the XXIX Physics in Collision, Kobe, Japan, August 30 - September 2, 2009